Scary. Wish I could help

 

It really sounds like it's pneumatic to me, pressures trying to equalize when the vacuum is removed, (engine turned off). Have you tried disconnecting the vacuum line to the brake booster? a significant amount of stored vacuum behind a check(one way) valve(plug the port/open line at engine side to prevent creating a large vac leak). Use this same strategy on the EVAP system. The service manual has some drawings that you may find helpful. Make sure the AC is turned off to eliminate it as a source. These tests may throw some codes, but they should clear when everything is hooked back up and the car is driven. Hope this helps.

 

car fart.

 

More like a queef lmao. j.k. All jokes aside undue the plenum spacer you have just installed and mabey you find your answer there .